A concrete cutter for cutting pavement or other structures, can include a heavy driver containing an engine which drives a diamond sawblade that can cut a groove in the concrete. It is important that the blade rotate about an axis precisely concentric with the central hole in the blade, which is in turn precisely concentric with the periphery of the blade. The diamond teeth each takes a small cut such as 1/10,000th inch, so a blade mounted off-center by over one or two thousandths inch would cut with much less than one-half of the blade periphery until the periphery were worn concentric with the rotation axis. In prior art machines, the output shaft of the driver has an outer shaft end which included a cylindrical projection of the same diameter as the central hole of the blade and which fits therein. An outer blade plate fits against the other face of the blade and is attached to the cylindrical projection at the outer end of the shaft. Since the shaft rotates precisely about its axis and the axis of its cylindrical projection, this arrangement assures that the blade will rotate precisely about its blade axis.
When cutting concrete or asphalt on hot days, a diamond blade often becomes "pinched" in the cut because of pavement expansion. In order to cut out the blade from the pavement, it is desirable to move the heavy driver out of the way. However, the driver is constructed to move only along a predetermined drive direction perpendicular to the shaft axis. As a result, the cylindrical projection at the end of the proir art shaft cannot be easily withdrawn from the hole of the blade. The driver is a heavy vehicle, typically weighing 1,000 to 1,500 pounds, so it is very difficult for the operator of the driver to move the machine sideways. An arrangement which permitted detachment of a stuck blade from the drive shaft, would aid in removing a pinched blade, saving many man hours of labor and much machine damage from moving the machine sideways.